Airbags in airbag modules are usually arranged in a folded state in an airbag housing behind a covering. In the event of a crash the airbag is inflated, i.e. filled with a gas. The airbag is deployed to form a gas-filled cushion that can damp the impact of the vehicle occupant. Up until now, folding of the airbag has been performed such that the airbag has been spread out flat and then folded specifically at predetermined points resulting in a folded arrangement. This folded arrangement is then arranged in the airbag module near the gas generator, or a gas-supply device, such that it is located in the direction of deployment of the airbag, i.e. the folded airbag is located between the gas generator and the vehicle occupant.
The methods which have been used heretofore for folding an airbag have a number of disadvantages. For example, a very large amount of space is necessary for the purpose of folding the airbag, since the entire airbag must first of all be spread out flat. Furthermore, for automated folding of the airbag, there is a need for a relatively complicated installation, which has to be adapted individually in each case to different airbag shapes and the specific folding sequences thereof. Moreover, such complicated folding can only be performed at a limited speed.
An object of the invention is to provide a method and an apparatus for folding an airbag for an airbag module and permit simplified and quicker folding of the airbag and a smaller amount of installation space for the apparatus.
In the method according to the invention, the airbag is first of all straightened out in the direction of a straightening axis, starting from a gas inlet opening of the airbag. In the straightened-out state or during the straightening-out operation, the airbag is pushed or drawn into an outer guide device in the direction of the straightening axis, and then the airbag is pushed together, and in the method folded up, within the outer guide device in the longitudinal direction thereof, i.e. in the direction of the straightening axis. In this method, for the folding operation, the airbag is straightened out along an axis rather than being spread out flat resulting in a three-dimensional arrangement. The subsequent folding operation does not take place in a specific manner, i.e. the airbag is not folded along precisely predetermined folding lines. Rather, folding is brought about arbitrarily by the airbag being pushed together in the outer guide device. The airbag is folded in the manner of an accordion, the fold lines being produced arbitrarily. This folding method permits the airbag to be folded considerably more easily and quickly since it is possible to dispense with numerous individual, precisely defined folding operations along predetermined folding lines. Furthermore, the method does not require much space since the airbag does not have to be spread out flat, but rather is straightened out along a line instead.
This folding method produces a folding pattern with main folding lines that start from a central region, which is located in the vicinity of the straightening axis, and run essentially radially outwards in a straight line to the periphery of the airbag. It is also possible to achieve folding in the case of which the main folding lines run essentially radially on the front layer of the material, which is directed toward the vehicle occupant, while they run essentially concentrically, preferably parallel to the periphery of the airbag and/or of the gas inlet opening, on the rear layer of material, which is directed away from the vehicle occupant.
The straightening axis advantageously runs essentially perpendicularly with respect to a front surface of the airbag. The front surface of the airbag in this case is the impact surface of the airbag, which, when the airbag is installed in a motor vehicle, is directed toward a vehicle occupant when the airbag is inflated. Since the straightening axis runs essentially perpendicularly with respect to said front surface, it is possible to ensure, on the one hand, a straightforward folding operation and, on the other hand, at a later stage, when the airbag is filled with gas by a gas generator, also a specific and reliable deployment operation of the airbag, in the case of which first of all the front surface moves toward and comes into contact with the vehicle occupant.
During the folding operation, the airbag is expediently fixed preferably in the region of its gas inlet opening. This makes it possible to ensure, during the folding operation, that the gas inlet opening remains free and is later accessible to be fitted on a gas-supply device or a gas generator.
The airbag is preferably pushed together in the outer guide device by means of a folding ram. In this case, the folding ram moves within the outer guide device along the longitudinal axis thereof, i.e. in the direction of the straightening axis, and pushes the straightened-out airbag together such that it folds up in the manner of an accordion. In this case, the individual folds or creases are produced of their own accord during the folding operation without precise folding lines being predetermined. Despite folding lines that are not precisely predetermined, a satisfactory, precisely controlled deployment of the airbag at a later stage can nevertheless be ensured.
For the purpose of straightening out the airbag, a straightening ram is advantageously pushed into the latter in the direction of the straightening axis, starting from the gas inlet opening, and comes into abutment, by way of its end surface, against the inside of a section of the airbag which is located opposite the gas inlet opening. This allows the airbag to be straightened out to the full extent. The airbag is straightened, by the straightening ram being pushed in, until further movement of the straightening ram is restricted as a result of limiting bands, tear seams, etc. arranged in the airbag or by the outer sheath of the airbag itself. In this case, the straightening ram advantageously moves in a straightening direction, which corresponds, to the later main deployment direction of the airbag. This means that the airbag is straightened in its main deployment direction. This makes it possible to ensure, during the later pushing-together operation, that the folding-up operation of the airbag takes place in reverse order to the operation in which the airbag has to unfold again at a later stage when being inflated.
In the folding pattern produced during the subsequent folding operation, the central region from which the main folding lines, i.e. the creases produced during folding, extend radially outwards essentially in a straight line is that region of the airbag which butts against the end surface of the straightening ram. Essentially no folding lines are then formed in this region. The folding lines may run in a precisely radial manner toward the center point of this region. However, it is also possible for them to run such that they border tangentially on the periphery of said abutment surface, which in the case of a circular end surface of the straightening ram is likewise essentially circular, and, starting from the periphery of the abutment surface, extends essentially in a straight line to the outer circumference of the airbag.
During the straightening-out operation of the airbag, the straightening ram is preferably simultaneously pushed into the outer guide device. This allows the time required for the folding-up operation to be reduced since the operations of straightening out the airbag and pushing it into the sleeve take place, at least in part, at the same time. Furthermore, the action of the straightening ram being pushed into the outer guide device with the airbag surrounding it achieves the situation where even regions of the airbag which cannot straighten out to the full extent as a result of, for example, limiting bands or seams, these are the peripheral or outer regions of the airbags for example, are likewise arranged in the outer guide device in the straightening direction or pushing-in direction.
Once the straightening ram has been pushed in, a positioning device is preferably advanced along the outside of the airbag, parallel to the straightening ram, starting form the gas inlet opening. This means that, before the airbag is folded, the rear region of the airbag, which surrounds the gas inlet opening, is positioned against the straightening ram. Once the airbag has been pushed together and folded up in the guide device, it is thus ensured that the parts of the airbag which are directed toward the vehicle occupant when the airbag is inflated are located on the outside or at the front, as seen in the deployment direction, in the folded airbag assembly. This means that, during the inflation operation, these parts of the airbag can spread out toward a vehicle occupant very quickly and without obstruction, as a result of which sufficient protection for the vehicle occupant can be ensured very quickly.
The positioning device is advantageously designed as a sleeve, which is concentric with the straightening ram or in the form of a plurality of bars, which are arranged around the straightening ram. Such a device can ensure that the airbag is correctly positioned against the straightening ram in its rear region. In this case, the distance between the sleeve or the bars and the straightening ram has to be dimensioned such that that part of the airbag which is to be placed in position can be received between the positioning device and straightening ram without getting caught or being damaged, and is positioned against the straightening ram as smoothly and uniformly as possible.
In a further embodiment, once it has been straightened out in the direction of the straightening axis, starting from the gas inlet opening, the airbag is drawn into the outer guide device in a direction counter to the movement direction of the straightening ram when the airbag is straightened out, the straightening ram accordingly being moved along in the same direction in order to keep the airbag in its straightened-out state. This achieves an effect similar to that achieved by the additional positioning device, although there is no need for any additional method steps or equipment. When the airbag is drawn into the guide device, part of the front side of the airbag, said front side being located opposite the gas inlet opening, is positioned against the straightening ram in the vicinity of the part which comes into contact with the end surface of the straightening ram. Furthermore, the peripheral connecting seams of the airbag are also arranged in the vicinity of the front side of the airbag. This can achieve the situation where, once the airbag has been pushed together in the guide device, the airbag is folded such that the front side of the airbag and the regions of the peripheral seams are located at the top. This means that when the airbag is deployed, when it is filled with gas, said regions are located at the front, as seen in the deployment direction, with the result that said regions, with which a vehicle occupant comes into contact in the event of a crash, are the first to unfold, with the result that good protective action is achieved very quickly.
During the pushing-together operation of the airbag, the folding ram is advantageously moved counter to the pushing-in direction of the straightening ram, while the straightening ram is simultaneously moved back preferably at the same speed. As a result of this movement sequence, the airbag is folded toward the gas inlet opening. This makes it possible to ensure that part of the airbag front surface, which is usually located opposite the gas inlet opening, is the last to be pushed onto the already folded airbag. This means that, during the later deployment of the airbag, first of all this relatively small and light part of the front surface is accelerated and then is moved toward a vehicle occupant. This movement of the front surface, or part of the front surface, is slowed down, during the deployment, by the still folded regions of the airbag, this resulting in quicker and predominantly radial and/or peripheral unfolding of the airbag.
Furthermore, during the pushing-together operation, it is possible for the folding ram to be moved in the pushing-in direction of the straightening ram, while the straightening ram is preferably not moved at all. In this procedure, the airbag is pushed together, and folded, toward its front surface. This can also ensure that the front surface of the airbag is the last to rest on the folded part of the airbag, since the front surface advantageously butts against the straightening ram during the entire folding operation. Meanwhile, the rest of the airbag is pushed together, and folded, along the outer walls of the straightening ram up to the front or end side thereof, against which the front side of the airbag butts. In this method, the airbag is preferably fastened on the folding ram in the region of the gas inlet opening, with the result that this part comes to be located at that end of the airbag, which is folded in the manner of an accordion, which is opposite the front surface. This means that the gas inlet opening is easily accessible, with the result that it can easily be arranged on a gas generator or a gas-supply device at a later stage.
Following the straightening-out operation and during the pushing-together operation the outside of that section of the airbag which butts against the end surface of the straightening ram is advantageously kept in contact with the folding ram or with part of a covering of the airbag module. This makes it possible for part of the airbag, preferably part of its front surface, to be clamped in between the straightening ram and the folding ram, or part of the covering of the airbag module, during the folding operation. This makes it possible to ensure that, following the folding operation, this part of the airbag is the last to rest on the folded airbag arrangement and can be arranged in the immediate vicinity of a gas generator. During the later inflating operation of the airbag, it is then possible to ensure that first of all this section, which was clamped in between a covering or the folding ram and the straightening ram, is set in motion without obstruction, with the result that, starting from this region, the airbag is unfolded during deployment in a uniform and controlled manner. The airbag is clamped in between the straightening ram and the covering if the airbag is folded directly inside a covering of an airbag module. At a later stage, in the installed state, the covering is then directed toward the vehicle occupant and has a corresponding tear seam, through which the airbag can deploy in the direction of the vehicle occupant. Following the folding-up operation an appropriate gas-supply device or a gas generator is introduced into the covering from the rear side. Another method variant is to fold the airbag inside an airbag housing. In this case, the airbag is first fastened on the airbag housing at the peripheral regions of the gas inlet opening. In this folding-up method, a region of the airbag is clamped in between the straightening ram and the folding ram and the folding ram is moved in the direction of the airbag housing. It is also possible in this method to ensure that the previously clamped-in region of the airbag is the last to rest on the other, already folded regions of the airbag. Last of all, the covering of the airbag module is fitted over this region of the airbag.
That section of the airbag against which the straightening ram butts by way of its end surface is advantageously part, and preferably a central part, of the front surface of the airbag. However, it is also possible for the straightening ram to straighten the airbag eccentrically or asymmetrically, it being possible for the airbag to be given an asymmetrical preferential outlet direction. This ensures that the section of the airbag which butts against the end surface of the straightening ram is secured and guided in a defined manner during a pushing-together and folding-up operation. Following the folding operation, the section of the airbag which butts against the end surface of the straightening ram is located directly behind the covering of the airbag module. During the later deployment of the airbag this section of the airbag will thus first of all break through the covering and move toward a vehicle occupant. This section of the airbag, which is advantageously the central region of the front surface, will be the first to come into contact with the vehicle occupant, while the airbag regions extending radially around this region come into contact with the vehicle occupant subsequently one after the other, i.e. starting from its central region, the airbag rolls on the vehicle occupant, advantageously his/her face. This makes it possible to avoid friction between the airbag and vehicle occupant, which friction could possibly result in grazing, since the vehicle occupant comes into contact with the airbag progressively in a precisely defined manner. This is particularly important if, during the deployment of the airbag, the vehicle occupant is not in a precisely defined position, i.e. in so-called out-of-position cases. This reduces the risk, which arises in the case of conventionally folded airbags, of the airbag getting caught, for example, beneath the vehicle occupant's chin during the deployment and minimizes the extension of a vehicle occupant's neck. The restraining action of the folded part of the airbag, which is still located in the airbag housing at the beginning of the deployment, slows down the emergence of the front surface. This results in this region of the airbag emerging to a correspondingly small depth, and the airbag then preferably quickly spreads out radially in front of a vehicle occupant. This reduces the risk of injury for the vehicle occupant during the deployment of the airbag.
During the pushing-together operation it is a desirable that a spacer be arranged in the airbag, preferably in the vicinity of the gas inlet opening. Such a spacer is necessary if a gas generator or a gas-supply device is not to be introduced into the airbag until after the folding-up operation. The spacer keeps free the installation space required for the gas generator or the gas-supply device. The airbag can thus easily be folded precisely such that it is later arranged, in the installed state, around the gas generator or the gas-supply device.
It is further preferred for the straightening ram to assume the function of the spacer. There is thus no need for any additional method step for introducing a spacer since the cavity necessary for the gas generator is kept free in the interior of the folded airbag by the straightening ram.
The airbag is preferably pushed out of the outer guide device into an airbag housing or into a covering for an airbag module. This makes it possible to ensure that, during introduction of the folded airbag into a covering or into an airbag housing, the airbag does not come out of its folded state prematurely.
It is further preferred for the airbag to be pushed into the airbag housing or the covering for the airbag module during the folding operation. This avoids an additional operation for introducing the folded airbag into the airbag housing or into a covering since the airbag is folded directly into the covering or the housing, by virtue of being pushed together in the sleeve and forced into the housing or the covering.
The apparatus for folding an airbag comprises a straightening ram which, for the purpose of straightening out the airbag, can be pushed into the latter in the direction of a straightening axis, by way of a gas inlet opening, also comprises a guide sleeve which is arranged coaxially with respect to the straightening ram and into which the straightening ram can be pushed along the straightening axis, it being the case that the inner cross-sectional surface area of the guide sleeve is greater than the cross-sectional surface area of the straightening ram, in particular greater by such an extent that the airbag can be folded up between the straightening ram and an inner wall of the guide sleeve, and also comprises a folding ram which, for the purpose of pushing the airbag together, can be moved within the guide sleeve along the straightening axis. This apparatus is suitable, in particular, for carrying out the above-described method. It has the advantage that it may be of extremely compact configuration since all the movements necessary for folding the airbag take place along one and the same axis, i.e. along the straightening axis, along which the airbag is straightened out. For as space-saving an arrangement of the apparatus as possible, the straightening axis runs, as far as possible, vertically. The guide sleeve and the rams are preferably of round design, but may also be of any other desired shape, which may be adapted, in particular, to a specific shape of the airbag or of the airbag housing or of the airbag-module covering. The standing surface of the apparatus according to the invention need not be much greater than the airbag housing, or the covering of an airbag module itself, since, for the purpose of folding the airbag, the latter is straightened out along an axis, i.e. a line in the direction perpendicular to the airbag housing or the covering, rather than there being any need for it to be spread out flat. Since in this case the airbag is straightened out into the guide sleeve, the cross-sectional surface area of the straightening ram is designed to be smaller than the inner cross-sectional surface area of the guide sleeve, with the result that the straightened-out airbag comes to be located between the straightening ram and the inner walls of the guide sleeve.
The folding ram preferably has a cross-sectional surface area that corresponds to the inner cross-sectional surface area of the guide sleeve. Sufficient play between the folding ram and the guide sleeve is nevertheless ensured in this case, in order that the folding ram can be moved easily in the guide sleeve along the longitudinal axis thereof. However, the folding ram butts so closely against the inner wall of the guide sleeve that it is not possible for regions of the airbag to pass into the gap between the folding ram and the inner wall of the guide sleeve, which could result in the airbag being damaged and the apparatus being blocked.
The folding ram advantageously has, preferably in its center, an opening through which the straightening ram extends. This arrangement makes it possible for the airbag, during folding inside a covering cap or covering, first of all to be straightened out, starting from its gas inlet opening, and then, likewise starting from the gas inlet opening, to be pushed together toward the opposite side of the airbag, i.e. toward the front surface. In this case, the folding ram moves along the straightening ram, which is guided in the opening of the folding ram and is preferably not moved at all.
Fastening devices are expediently provided for fastening the airbag preferably in the region of its gas inlet opening. This allows the airbag to be retained securely during the folding operation, and it is ensured that the gas inlet opening of the folded airbag is freely accessible, in order to be connected to a gas generator or a gas-supply device.
The fastening devices are preferably provided on the folding ram. This makes it possible, when the folding ram is displaced along the straightening ram for the pushing-together and folding-up operations for the airbag to be firmly secured on the folding ram, with the result that a section thereof is freely accessible for later fastening on an airbag housing. This section for fastening the airbag is advantageously located in the vicinity of the gas inlet opening, with the result that the latter can be fixed precisely on a gas-supply device or a gas generator.
It is also possible for devices to be provided in order to keep an airbag housing or a covering of an airbag module in contact with the guide sleeve. This means that the guide sleeve is advantageously forced up against the airbag housing or the covering, with the result that, during the folding-up operation of the airbag, the latter can be forced or folded directly into the airbag housing or the covering of the airbag module. This makes it possible to avoid, at a later stage, further operations for introducing the folded airbag into the airbag housing or the covering.
There is preferably provided a positioning device in the form of a sleeve or of a plurality of bars which are arranged coaxially, concentrically and at a distance from the straightening ram and, for the purpose of positioning the airbag against the straightening ram, can be moved parallel to the straightening ram. Such an apparatus makes it possible for a sub-region of the airbag to be positioned against the straightening ram before the airbag is folded. In order to achieve folding in the case of which the regions of the airbag which are directed toward a vehicle occupant when the airbag is deployed are located at the top of the folded assembly. This means that, during inflation of the airbag, these regions are the first to unfold, doing so without obstruction, as a result of which the greatest possible level of protection for a vehicle occupant can be achieved very quickly.